This invention relates to a component for an air braking system, and particularly to a combined air dryer/reservoir for a vehicle air braking system.
Air braking systems are typically found on heavy commercial vehicles. They usually comprise a compressor, a demand valve, one or more reservoirs and plurality of actuators for the vehicle wheel brakes. One common addition to an air braking system is an air dryer. An air dryer typically comprises a canister of desiccant downstream of the compressor and through which air is passed to the system. In time, the desiccant becomes less effective, as moisture is adsorbed, and it is necessary to regenerate the desiccant for example by reverse flow of dry air and exhausting the resultant moist air through a vent valve to atmosphere. Regeneration for a single chamber reservoir is carried out when the compressor is off-load using dry air from the system volume or from a dedicated purge tank downstream of the air dryer. Alternatively, parallel air dryers can be provided where little off-load time is available; regeneration for either one of the air dryers is carried out when the compressor is on-load and connected through the other air dryer; dry air is supplied to the xe2x80x98wetxe2x80x99 air dryer from a secondary downstream reservoir.
A typical air system lay out with a single air dryer is shown schematically in FIG. 1. The system comprises, in series, a compressor 10, an air dryer 12, a sensing tank 14 and reservoirs 16, 18 downstream of non-return valves 20,22 respectively. A pressure sensor in the tank 14 causes the compressor to be brought on load or off load according to the sensor state, and consequently to switch the air dryer inlet between pressure feed from the compressor and exhaust whereby dry air flows back through the desiccant chamber. The system shown requires rather a lot of piping to connect the individual components; it is not particularly compact and is consequently disadvantageous where space is limited.
It is an object of the invention to provide an improved component including air drying means for an air braking system.
Accordingly there is provided a component of an air braking system comprising a container having first and second compartments, the first compartment having an upstream inlet for connection to a source of air under pressure, a vent for connection to the exterior of the container and a desiccant therein, the second compartment comprising a chamber having a downstream inlet from the first compartment with non-return means therein, a return connection to the first compartment having a fluid restrictor therein, and an outlet for connection to an air braking system.
In that way the desiccant compartment is located next to the air reservoir constituted by the second compartment, which results in a much more compact system in which the external shape of the component can be adapted to the available space. The component of the invention is suitable for air braking systems in which the desiccant is regenerated when the compressor is off load but working and systems where the desiccant is regenerated whilst the compressor is deactivated. Furthermore the component of this invention can be used in systems which have significant compressor off load time, and systems where off load time is restricted and thus switching between alternative desiccant beds is required.
Preferably the component includes a control valve to regulate the passage of air through said upstream inlet and vent, and the control valve may be mounted to the container. The control valve may be controlled by a conventional demand valve signal such that regeneration of the desiccant is initiated at a suitable time.
In an alternative embodiment the component may include a third compartment having an upstream inlet for connection to a source of air under pressure, a vent for connection to the exterior of the container and a desiccant therein, the second compartment also having a downstream inlet from the third compartment with non-return means therein, and a return connection to the third compartment having a fluid restrictor therein. Preferably a control valve is provided to regulate the passage of air through the upstream inlet and vent of said third compartment. A common control valve may be provided to regulate the passage of air through said upstream inlets and vents of said first and third compartments. In that way air can be directed between the first and third compartments and thus permit a relatively wet desiccant compartment to be regenerated with dry air whilst air under pressure is supplied through the relatively dry desiccant compartment.
Preferably the control valve is adapted to selectively direct air to the upstream inlet of the first compartment and to the upstream inlet of the third compartment. The control valve may be adapted to direct air between said upstream inlets according to a timer, a sensing device adapted to monitor the degree of moisture in said first and third compartments, or any other suitable sensor.
Preferably the compartments are defined by a partition within the container and the first compartment may project into the second compartment. Where two desiccant chambers are provided, both may project into the air reservoir constituted by the second compartment.
There may be provided a further compartment comprising a chamber connected to the outlet of said second compartment, non-return means being provided at said outlet and said further compartment being provided with a supply connection to an air braking system. This arrangement places successive air reservoirs in series, the upstream reservoir constituting a relatively small reservoir for desiccant drying purposes, and the downstream reservoir constituting a main supply tank for the braking system.
The component is preferably modular, most preferably in the form of a canister for installation into an air braking system. In such a case the inlets and outlets may have appropriate pressure fittings. The component may for example be screw threaded onto a valve block in a manner similar to that of an oil filter.
The desiccant may be removable from the first and third compartments.
The invention also encompasses an air braking system, particularly a vehicle air braking system, having a component according to the invention.